Cause and effect analysis

July 25, 2006

It would be easy to leap to the conclusion that higher interstate speeds in Indiana have led to a dramatic increase in fatalities on those highways. Since the Indiana General Assembly voted to increase the speed limit to 70 mph on the state's six interstates, traffic fatalities have shot up 40 percent. Blaming the increase on the speed limit increase would indeed be alarming, but would it be accurate? During that same year that the Indianapolis Star analyzed the interstate figures, statewide traffic deaths actually declined from 897 to 836. To further confuse matters, the Indiana State Police report that troopers issued 10 percent more speeding tickets along those stretches of highways with speed limits of 70 mph. Overall the total number of crashes dropped from 209,500 to 177,800. It seems that police are doing a good job of enforcement, so maybe there's another answer. Police rightly point out that looking at one year's worth of statistics can be misleading. In order to get an accurate picture, several years of data would have to be examined. Other factors also would have to be considered, such as weather conditions, traffic volume and road construction. It should not be immediately assumed that there is a cause and effect connection between higher interstate speeds and more deaths. The increase could even turn out to be an anomaly. We encourage the Indiana Department of Transportation to begin a careful study to determine the exact cause of the increase in traffic fatalities. If it can be proven that higher speed limits are indeed resulting in higher driving speeds and that those speeds are, in fact, contributing to higher accident rates and greater damage, then something can be done about it. It seems to us that there is not enough information to reach that conclusion right now.